First, yes it is probably more common to shim at an early stage rather than later, as the valves seat in they get tighter and may need to be shimmed. If you continue to ride like it is you'll need another new motor. Change the piston to an aftermarket, I like Wiesco, the 06 had an issue with the piston breaking. Tight vavle is probably why it doesn't want to start. Remember when your selling something you can say whatever you want to, who's going to challenge you, an 06 with 10 hours, hmmmm, pretty tough to swallow. maybe 10 hours since the person put an hour meter on it.